Mixer for use with microwave oven

ABSTRACT

A mixer, primarily for thawing frozen biological materials, is adapted to use the turntable mechanism of a microwave oven (33), a container (4, 30) being carried round by the turntable mechanism (34) and being simultaneously rotated about a transverse axis. In one version the container is a cylindrical drum (4) carried by a cradle (3) which replaces the turntable. A transmission (5) such as friction wheels (13, 14) or gears (17, 18; 20) between the drum and fixed structure (17; 19; 22) within the oven causes the drum to rotate about its axis as the cradle is turned. Alternatively, the container (30) is spherical and the turntable (34) tilts so that the container is biassed to one wall (35) of the oven. But rotation of the turntable causes it to co-operate with other walls (37, 38) and thereby generates a tumbling action.

This invention relates to mixers. It is primarily intended for a mixerwhich can be inserted into a domestic microwave oven, for example toachieve uniform and controlled thawing of frozen material.

Current medical practice often involves the thawing of frozen biologicalmaterials, and microwave radiation is sometimes used to achieve this.When this is done using a domestic microwave oven, rotation of thematerials being thawed is usually performed in the horizontal plane byway of a motor-driven plate at the base of the oven, or alternatively inthe vertical plane by way of a side-pivoted side-driven cradle. Neithermethod optimises the uniformity of radiation exposure, although thevertical method does contribute a tumble-mix component, once thawing isinitiated. Non-uniform exposure of some frozen biological materials tomicrowave radiation may lead to heat-denaturation of the same in theareas of maximum exposure. The present invention was developed in orderto minimise this problem, using a domestic microwave oven with centralbase-plate motor drive to achieve simultaneous horizontal and verticalaxis rotation of the materials to be thawed. This optimises theuniformity of exposure of materials to microwave radiation, and alsoprovides simultaneous tumble-mixing of the materials.

According to one aspect of the present invention there is provided amixer for use with a microwave oven having a turntable, comprising aclosable container for receiving a charge of material to be mixed, andstructure for fixing within the oven for co-operation with the containeras the latter is carried around by the turntable rotating means, suchco-operation being arranged to rotate the container about an axistransverse to that of the turntable.

In one preferred form the container is a generally cylindrical drum withits axis horizontal, journalled in a cradle which is carried round bythe turntable rotating means. The co-operation may then be provided by atransmission between a member co-axial with the drum and an annular pathtraversed by that member. This transmission may include an intermediatewheel carried by the cradle and engaging said member and said path. Theelements of the transmission may have frictional engagement orinterengaging gear teeth.

The structure may include a base plate for resting on the floor of theoven, the cradle being carried by the plate and adapted for engagementby the turntable rotating means through an opening in the plate, theactual turntable having been removed. For stability and location, thecradle will conveniently have rolling means which run on the peripheryof said opening, and the cradle may lie within that opening. The annularpath may be provided by the base plate.

In an alternative construction, the container is spherical and thestructure comprises surfaces on the interior walls of the oven forsuccessive engagement by the sphere as it is carried around by theturntable, there being means for imparting a bias to the sphere so thatthere is a preferred surface of engagement, each surface when engaged bythe sphere being capable of imparting a rolling motion thereto.

This bias is conveniently a tilt imparted to the turntable. The surfaceimmediately upstream of the preferred surface in relation to thedirection of rotation of the turntable will preferably be spaced fromthe axis of the turntable a distance equal to the radius of thecontainer, while said preferred surface will be spaced from the axis ofthe turntable a distance greater than that radius.

According to another aspect of the present invention there is provided amethod for mixing and heating material, comprising encasing the materialin a container, placing the container in a microwave oven, the ovenhaving a turntable, and operating the oven, the container being carriedaround by the turntable rotating means and, by engagement with staticstructure within the oven, being caused to rotate about an axistransverse to that of the turntable.

Generally the container and structure will comprise a mixer as definedabove.

This mixer and method are particularly suited to the thawing of frozenbiological material.

For a better understanding of the invention, some embodiments will nowbe described, by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic perspective view of a drum mixer for use with amicrowave oven equipped with a turntable,

FIG. 2 is a perspective view of a drum support cradle forming part ofthe mixer,

FIGS. 3(a) and 3(b) show alternative transmissions for generatingrotation of the drum about its axis from the rotation of the turntabledrive.

FIG. 4 is a diagrammatic front view of a microwave oven with a turntableand a spherical mixing vessel,

FIG. 5 is a diagrammatic plan view of the oven of FIG. 4, and

FIG. 6 is a diagrammatic side view of the oven of FIG. 4.

The mixer has a square base plate 1 with a circular hole 2, and in useis set on the floor of a microwave oven (not shown) with the holecentred on the drive spindle of a turntable. The latter will have firstbeen removed.

A cradle 3, most clearly shown in FIG. 2, sits in the hole 2 and isrotated by the turntable spindle. It carries a drum 4 with its axishorizontal, and the rotary motion of the cradle 3 is used by atransmission 5 to generate simultaneous rotation of the drum 4 about itsaxis.

The cradle 3 in plan view is in the shape of a cross with one opposedpair of arms 6 being equipped at its ends with rollers 7 which bear onthe upper surface of the base plate 1. The other pair of opposed arms 8have upstanding pillars 9 at their ends with L-shaped slots 10 toreceive stub-shafts 11 at the ends of the drum 4. The shape of the slots10 is such that the drum is mounted by being moved horizontally and thenlowered to become captive.

Below the centre of the cross there is a boss 12 which is shapedunderneath to be engaged by the upper end of the turntable spindle, andbe rotated thereby, thus causing the cradle 3 and the drum 4 to turnabout a vertical axis.

At one end of the drum, one of the shafts 11 is fitted with a frictionwheel 13 which lies outside the pillar 9 when the drum is properlymounted, and this wheel 13 then engages another friction wheel 14carried by a pin 15 lower down on the outside of the pillar 9. The wheel14 bears on the base plate 1, and so as the cradle 3 is rotated, so thewheel 14 is turned. The frictional engagement with the wheel 13 causesthe drum 4 to be rotated about its axis. Thus, the contents of the drumwill be subject to a tumbling action as the drum is rotated about twomutually perpendicular axes.

Outside the pillar 9 at the opposite end from the transmission 5 (notvisible in the Figure) there will be a roller similar to the rollers 7,so that the cradle will be stably supported at the ends of all the arms.

The drum has closed ends 16, each fitted centrally with one of theshafts 11. Access to the drum may be by removal of one or both of theseends 16, and conveniently they may have screw fitting to the basiccylinder. However, it will be understood that many other forms ofattachment are possible, and a manual press-fit may be sufficient.

The inside of the drum may be equipped with blades or other means foraccentuating the mixing action.

It is envisaged that virtually the entire mixer may be made fromplastics material, and in certain circumstances where it is useful toknow how the mixing is progressing the drum may be of clear plastics.

The transmission 5 may take various other forms, and two examples areshown in FIG. 3. In FIG. 3(a), gear wheels 17 and 18 replace thefriction wheels 13 and 14, while the plate 1 is equipped around theperiphery of the hole 2 with teeth 19 to provide positive engagementwith the wheel 18. The rollers 7 will be arranged to run inside oroutside the teeth 19.

In FIG. 3(b) there are no interengaging wheels; instead one end 20 ofthe drum is made larger than the other and formed with gear teeth aroundits periphery. Once the drum is mounted, a frame or plate 21 can belowered to a fixed position overhead so that an annular array of teeth22 on the underside of the member 21 is engaged by the wheel 20.

FIGS. 4 to 6 show an alternative mixer where the mixing vessel is asphere 30 made by joining two substantially identical hemispheres 31 and32. These can be screwed apart, for example, to load the charge to bemixed. The size of the sphere 30 will be related as described below tocertain features of the interior of a microwave oven 33 in order toachieve the desired composite rotation.

The oven 33 has a turntable 34, but instead of being horizontal a tiltis imparted, as shown in FIG. 6, so that the sphere 30 which rests onthe turntable will always tend to roll down towards the front wall 35,its point of contact with the turntable then being off-centre and downthe slope. At the zone of contact with the wall 35, there is a frictionpad 36 to promote rotation of the sphere as it is carried round by theturntable in the direction of arrow A. To keep the sphere in compositeand random rotation, the side walls 37 and 38 are also provided withfriction pads 39 and 40 respectively. That on the wall 37, which isupstream in relation to the front wall 35 and the direction of rotationof the turntable, projects into the oven so that the centre of thesphere cannot move nearer the pad 39 than the vertical fore and aftplane through the centre of the turntable. This prevents the spherebecoming stuck in the bottom left hand corner as viewed in FIG. 5. Theopposite pad 40, however, on the side wall 38 is more remote and outsidethe radius of the turntable.

The tilt is shown as being imparted by a wedge 41 under the rear of theoven, but there may be more sophisticated arrangements, and an ovencould be constructed where its main body would be set level but with itsfloor and turntable sloping. Also the slope need not be to the front.

It is important that the centre of gravity of the loaded sphere shouldbe at its geometrical centre. Generally, the charge will be small inrelation to the complete sphere, and one solution to this is to fit thetwo hemispheres 31 and 32 to opposite sides of a disc or "spider" 42,shown in broken lines in FIG. 5, at the centre of which there is acapsule 43 or other means of holding the material to be mixed.

The friction zones (including the surface of the turntable) are shownshaded when viewed face-on. They may be provided simply by adhesivetape, and in some ovens and with certain container surfaces, it may evenbe possible to dispense with such measures to enhance the friction.

This arrangement ensures that, as the turntable rotates, the tendency ofthe sphere to move with the turntable is partially counteracted bygravity and the friction between the sphere and oven walls. Theinterplay of forces leads to random rotation of the sphere provided thatthere is enough friction for the forces between the interacting surfacesto be effective to promote rolling, and yet to not such an extent as toprevent some degree of slippage.

While gravity is the simplest means of biassing the sphere towards onewall, it is possible that other means could be used. For example, ablower inside the oven could urge the sphere constantly in onedirection, or magnetic attraction or repulsion could be employed.

I claim:
 1. A mixer for use with a microwave oven, said mixer comprisingan openable and closable, generally cylindrical drum and a cradle, saiddrum being journalled in said cradle, said cradle having means forengaging a turnatable drive spindle of a microwave oven to rotatetherewith and to permit rotation of said drum with said drive spindleabout an axis extending transversely through said drum as said drivespindle rotates said cradle, roller means carried on said cradle to reston and to roll in a circular path on a stationary, flat surface as saiddrum and cradle are rotated by said drive spindle, and transmissionmeans including at least some of said roller means for causing said drumto rotate about its own longitudinal axis as it rotates with said drivespindle.
 2. The mixer of claim 1 in which said generally cylindricaldrum is adapted to be positioned in a microwave oven with its axisperpendicular to the axis of the drive spindle of said microwave oven.3. The mixer of claim 1 in which said tranmission also includes also atleast one wheel attached to said drum in a generally coaxial relation tothe longitudinal axis of said drum, said wheel being rotationally linkedto said roller means of said transmission whereby, as said roller meansrolls in its circular path on said flat surface, said wheel is rotatedby said roller in a corresponding manner to rotate said cylindricaldrum.
 4. The mixer of claim 3 in which said wheel and said roller meansof said transmission are linked together, and are adapted to be linkedto said flat surface, in frictional engagement.
 5. The mixer of claim 3in which said wheel and said roller means of the transmission arecircular gears with peripheral, interengaging teeth, and a circular geartrack is provided on said flat surface for engagement by said rollermeans of the transmission as it is rotated in its circular path.
 6. Themixer of claim 1 which includes a base plate for resting on the floor ofa microwave oven, said cradle being carried by said base plate inrotational relation with said base plate, said base plate defining acentral opening to permit connection of the cradle with a drive spindleof a microwave oven.
 7. The mixer of claim 6 in which said cradle lieswithin the opening of said base plate, and said flat surface which theroller means of the transmission engages is defined by such base plate.8. A mixer for use with a microwave oven, comprising an openable andcloseable, generally cylindrical drum and a cradle, said drum beingjournalled in said cradle, said cradle having means for engaging aturntable drive spindle of a microwave oven to rotate therewith and topermit rotation of said drum with said drive spindle about an axisextending transversely through said drum as said drive spindle rotatessaid cradle, roller means carried on said cradle to rest on and to rollin a circular path on a stationary, flat surface as said drum and cradleare rotated by said drive spindle, and transmission means including atleast some of said roller means for causing said drum to rotate aboutits own longitudinal axis as it rotates with said drive spindle, inwhich said transmission means also includes at least one wheel attachedto said drum in a generally coaxial relation to the longitudinal axis ofsaid drum, said wheel being rotationally linked to said roller means ofsaid transmission whereby, as said roller means rolls in its circularpath on said flat surface, said wheel is rotated by said roller in acorresponding manner to rotate said cylindrical drum, said mixer alsoincluding a base plate for resting on the floor of a microwave oven,said cradle being carried by said base plate in rotational relation withsaid base plate, said base plate defining a central opening to permitconnection of the cradle with a drive spindle of a microwave oven, saidbase plate also defining the flat surface which the roller means of thetransmission engages.
 9. The mixer of claim 8 in which said generallycylindrical drum is adapted to be positioned in a microwave oven withits axis perpendicular to the axis of the drive spindle of saidmicrowave oven.
 10. The mixer of claim 9 in which said wheel and saidroller means of said transmission are linked together, and to said baseplate, in frictional engagement.
 11. The mixer of claim 8 in which saidwheel and said roller means for the transmission are circular gears withperipheral, interengaging teeth, and a circular gear track is providedon said base plate for engagement by said roller means of thetransmission as it is rotated in its circular path.